Damage is usually caused in
the spring when the larvae or maggots burrow into seeds or
seedlings. Larvae begin feeding on germinating seeds or organic
matter soon after hatching. Partially decayed seeds, injured
seeds, or poorly healed potato pieces are favorite foods. Larvae
feed within and destroy the seed. Failure of seed germination or
seedling emergence is usually the first sign of infestation.

Attacked beans that sprout
often show a "Bald-headed" condition (a plant without
primary leaves) or severely damaged primary leaves. This results
in stunted plants, deformed beans and reduced yields.

Corn seedlings damaged by
this pest are weak and sickly. Typical symptoms are curling,
drying, or dead leaves.

Seed potatoes are often
attacked if they are bruised, decaying, or diseased. Damage to
these fields usually covers large areas and occasionally most of
the field. When there is heavy feeding of maggots, replanting may
be necessary.

Development of seedcorn
maggots from egg to adult occurs in 21-40 days. Depending on
climatic conditions, there are 1-5 generations per year (Higley
& Pedigo, 1984).

EGGS

Eggs are deposited close to
seeds in soil where there is abundant organic matter, seeds, or
plant seedlings. Recently worked soil tends to be favored for egg
deposition. Adult females lay an average of 100 eggs over a 3-4
week period. Eggs are elongate, pearly white, with a reticulate
pattern. Under normal field conditions, eggs hatch in 2-4 days.

LARVAE

Larvae are small maggots,
yellowish white to dirty yellow, legless, and measuring
approximately 1/5 inch in length and 1/25 inch in girth in their
later stages. Seedcorn maggots have three larval stages. Larval
development is completed in 12-16 days.

PUPAE

Mature larvae pupate in the
first 2-3 inches of soil a short distance away from the host
plant. Pupae are tan to brown and less than 1/4 inch long. They
are approximately three times as long as wide. The pupal stage
lasts from 7-20 days, depending on temperature.

ADULTS

The grayish brown adult
flies are about 1/5 inch long and are often mistaken for small
houseflies. Adults may live for 4-10 weeks.

Young larvae are active
after emergence. Although occasionally found alone, they usually
occur in masses of up to 100 larvae. Feeding begins as soon as a
food source is found.

Adults feed upon the nectar
of flowers of a number of cultivated and wild plants. Adults are
active in the mid-morning, especially when temperatures are
between 60û-85ûF. They are inactive at night. Strong winds and
rain reduce adult activity. The fly may frequently be seen
hovering over plants upon whose flowers they feed on and other
objects. Their flight pattern is a series of hovering and darting
in different directions. They are attracted to odors from
alcohols and sweet, fermenting substances (Reid, 1940).

The greatest damage occurs
in cool, wet seasons and in soils containing large amounts of
organic matter.

NON-CHEMICAL CONTROL

A preventive measure
against seed corn maggot infestation is to plant when the soil
and weather promotes rapid germination. Planting in highly
organic soils, wet soils, or during wet weather periods should be
avoided whenever possible as this often leads to increased
problems. If using manure, let it age and incorporate it
thoroughly into the soil. Severely damaged stands may be reseeded
with little danger of reinfestation.

Sanitation practices such
as removal of flowering weeds from outlying areas to eliminate
nearby food sources for adult flies and removal of sweet smelling
substances decreases the attractiveness of an area to these
flies. However, this action also reduces nectar sources for
beneficial insects.

Because much of its life
cycle is passed protected underground, seedcorn maggots do not
appear to have a great number of natural enemies (Reid, 1940).
Isolated incidences of predation by spiders and birds upon
adults, and fungus diseases on the larvae have been reported.
However, none of these predators are considered significant in
controlling seedcorn maggot populations.

The best way to prevent
damage to potatoes is to plant well suberized or healed potato
seed pieces. Areas and equipment used for cutting and storing
seed pieces should be disinfected and free from damaging bacteria
and diseases.

CHEMICAL CONTROL

Preventive treatments with
insecticides is the only effective way of controlling these
maggots in most seeds. Either a granular or seed treatment may be
used. Seed treatment is one of the least expensive and most
effective treatments for control of seedcorn maggot. The use of
some fungicides has reduced seed piece damage and subsequent
maggot damage.

Hardy, D. E. 1981. Hylema
(Delia) platura (Meig.) pp. 36-38. In Insects of
Hawaii. A Manual of the Insects of the Hawaiian Islands,
Including Enumeration of the species and Notes on Their Origin,
Distribution, Hosts, Parasites, etc. Volume 14, Diptera:
Cyclorrhapha IV, series schizophora, section calyptratae. The
University Press of Hawaii. Honolulu. 491 pages.